1. Field of the Invention
The present invention relates to a navigation apparatus for guiding a vehicle to a destination, and more particularly, to a navigation apparatus for preventing difficulty in viewing a navigation route when the navigation route is shown in a map displayed on a screen and is obstructed by buildings and the like that are three-dimensionally displayed on the screen.
2. Description of the Related Art
A navigation apparatus includes a map/information storage medium such as a CD-ROM, DVD-ROM, and the like in which map data for drawing a map and facility information data for searching facilities and the like are recorded, a replay unit for reading data from the map/information storage medium, a display unit for displaying a map and the like, and a vehicle position detecting unit for detecting a present position and a traveling direction of a vehicle using an integrated navigating system such as a distance sensor, gyro and the like and a GPS receiver and the like. The navigation apparatus reads out map data around the present position of the vehicle from the map/information storage medium, draws a map image of the vicinity of the vehicle position based on the map data on a screen of the display unit, displays a vehicle position mark by superimposing it on the display screen, and scrolls the displayed map image as the vehicle moves or moves the vehicle position mark while fixing the map image on the screen so that the present vehicle location can be found instantly.
The map data stored in the map/information storage medium such as the CD-ROM, DVD-ROM and the like is separated into longitude sections and latitude sections each having a proper width according to various levels of reduction scale. Roads and the like are stored as sets of coordinates of nodes expressed by longitudes and latitudes. A road is composed of at least two nodes connected to each other, and the map data is composed of a road layer, which includes a road list, a node table, an intersection constituting node list and the like, map data such as a background layer and the like for displaying roads, buildings, facilities, parks, rivers, and the like on a map screen, and information data for displaying characters, map symbols and the like of the names of administrative districts such as the names of local authorities, the names of roads, intersections, facilities, and the like.
An image combining unit appropriately combines the above data, displays a map, and three-dimensionally displays, for example, landmarks indicating characteristic buildings, surrounding buildings, and facilities as necessary so that the situation of a present position can be easily understood on a map. Further, a user can drive the vehicle while easily ascertaining a present vehicle position by comparing the surrounding situation that the user observes with an image displayed on a monitor screen. In particular, with improved processing speed and advanced image display technology, satisfactory three-dimensional images of buildings on a map have been achieved in recent navigation apparatuses, and many navigation apparatuses are used to display surrounding buildings three-dimensionally while displaying a map as if from a bird's-eye view.
Further, the navigation apparatus has a route guiding function for enabling the user to easily drive the vehicle to a desired destination without traveling on a wrong road. According to the route guiding function, a destination and waypoint locations are set by various means using an address, phone number, scrolling of a map, landmark nearby, and the like, and a proper route is calculated and presented by adding various conditions to routes connecting these locations from a start point to the destination. A route selected by the user is stored as a navigation route and displayed on the screen by being drawn using a thick line with a color different from that of other routes while the vehicle travels. Further, when the vehicle comes near to an intersection within a predetermined distance where it must change a course on the navigation route, the intersection is displayed in enlargement, an arrow or the like which indicates a direction in which the course of the vehicle must be changed is drawn and displayed on the screen, and voice guidance for guiding right and left turns is supplied to the user so as to guide the user to the destination.
When the navigation route as described above is calculated, there are available various kinds of route calculation systems that calculate, for example, a route through which the user can reach the destination from the present position in a shortest time, a route having a shortest traveling distance, a route making use or not making use of a highway and other toll roads, and so on. Of these route calculation systems, when there is a route calculation system designated by the user through a menu screen, the navigation apparatus presents an optimum route calculated by the designated calculation system to the user. Further, when no calculation system is designated by the user first, the navigation apparatus may display the routes calculated by the respective calculation systems on the screen with a different color, and the user selects and determines a desired route therefrom.
In the navigation apparatus arranged as described above, the navigation route calculated and determined as described above is displayed by being superimposed on a road of a map displayed on the monitor screen. At this time, when the displayed map is a two-dimensional map, the user can observe the navigation route as it is. As a result, the user can easily and distinctly observe an area ranging from a present position of the vehicle to a location existing in a traveling direction.
However, in recent years, many navigation apparatuses have been used to display a map as if from a bird's-eye view, and surrounding buildings are displayed substantially opaquely and three-dimensionally. Accordingly, when for example as shown in FIG. 6, a navigation route G extends forward on a road R1 from a vehicle position mark P, makes a right turn at an intersection C1 displayed as EBISU MINAMI INTERSECTION in the figure, travels straight on a road R2, makes a left turn at a next intersection C2, and travels straight on a road R3 on a map in which buildings are three-dimensionally displayed, the road R2 cannot be observed because it is obstructed by buildings in front of it. Thus, a problem arises that the navigation route G displayed on the road R2 almost cannot be observed.
As a countermeasure to the above problem, there is a system for three dimensionally displaying buildings and the like on a map using transparent frames and properly color coding them so that a road and a navigation route displayed thereon can be observed. In this display method, however, when the buildings are displayed transparently so that the navigation route and the like can be distinctly observed, the appearance of the buildings purposely displayed three-dimensionally is difficult to see, and thus displaying buildings three-dimensionally becomes meaningless. On the other hand, displaying the buildings so that the appearance thereof can be distinctly observed makes it difficult to observe the road and the navigation route. That is, a distinct display of buildings is incompatible with that of a road and a navigation route, and it is substantially impossible to coordinate the distinct display of the appearance of the buildings with that of the navigation route.